The present invention relates to a sheet deposition device for the selective deposition of printed sheets on a number of superimposed supports wherein each support is provided with its own drive means for moving said support up and down between a deposition position in which sheets can be deposited on that support and a parking position in which sheet deposition is not possible.
A sheet deposition device of this kind is known from European Patent 0 532 069. In this known sheet deposition device, when a predetermined maximum number of sheets has been deposited on one of the supports, a change-over can be made to the further deposition of sheets on one of the other supports, provided there are no sheets present on said other support, and this can be detected by a detector at the support surface of a support. During the displacement of a support, which is necessary for the purpose, with the maximum number of sheets thereon, to a lower parking position, said support will come entirely outside the deposition range of a support subsequently placed in the deposition position, in order to prevent the latter support from colliding, in its deposition position, against the sheets on the support which has been set to its lower parking position and would therefore be obstructed in its further movement.
The object of the present invention is to provide a sheet deposition device wherein a support is movable between the deposition position and the parking position provided that there is still free space for movement between the superimposed supports and without the supports, possibly with sheets therebetween, jamming against one another. To this end, according to the present invention, a support is provided with detection means for detecting an obstacle in the space directly therebeneath, for example sheets on a support directly therebeneath, which detection means delivers a first detection signal, when the distance between the support provided with said detection means and an obstacle therebeneath is greater than a predetermined amount, and delivers a second detection signal, when said distance is equal to said predetermined amount. The sheet deposition device comprises a control device which in response to reception of a first detection signal makes the drive means capable of activation for moving towards one another the supports between which are situated the detection means delivering the first detection signal and which deactivate the said drive means in response to the reception of a second detection signal.
According to one aspect of the present invention, the detection means comprises a flat plate suspended beneath a support and movable between a first position in which the plate is situated at some distance from and parallel to said support and a second position in which the plate is situated at an even shorter distance from said support. The detection means further comprises switching means between the plate and the support with actuating means which are rigidly connected to the movable plate and in the first position of the plate actuate the switching means to deliver the first detection signal and in the second position of the plate actuate the switching means to deliver the second detection signal.
The effect of the flat plate is that an obstacle beneath a support can be detected over a relatively large range, this being important particularly if the object is a stack of sheets on a support situated directly beneath the relevant support, which does not have a flat top, for example, because the stack consists of stapled sets which have a relatively considerable thickness at the staple position.
Preferably, the plate is provided with fixing means near its opposite edges, which connect the plate to the support for movement in the vertical direction and switching means are provided at each of said fixing means. The effect of this is that an obstacle can be readily detected at any place beneath a support without considerable room for movement for the plate being necessary for this purpose.
Preferably, one of the detecting means further comprises a U-shaped strap, of which the intermediate piece connecting its arms is connected for rotation about its longitudinal axis to one of the plates or supports for connection and the ends of the arms are rotatably connected to the other plate or support for connection. The effect of this is that during its movement from the first position to the second position the plate can tip in only one direction so that for the detection of an obstacle up to the four corner points of the plate it is only necessary to use two switching means near the fixing points in a central zone of the plate.
This gives a compact-constructed and flexible sheet deposition device in which supports with any sheets deposited thereon cannot jam against one another.
According to another aspect of the present invention, the control device of the sheet deposition device comprises control means which in response to the reception of a first detection signal delivered by the detection means at a support in a deposition position or a support therebeneath, make the drive means of said supports capable of activation for moving said support(s) downwards on deposition of the subsequent sheets on said support. As a result, sheets on a support in its parking position can lie within the range of deposition positions of a support thereabove, such range being increased when sheets are removed from the support in its parking position. Another effect is that deposition of sheets can be continued as long as there is anywhere free room for movement beneath the support in the deposition position.
According to yet another aspect of the present invention, the control device comprises control means which, upon displacement of a support from a parking position to its deposition position and in response to the reception of a first detection signal delivered by the detection at another support situated between the said parking position and the deposition position, makes the drive means of said other support or supports capable of activation for joint downward or upward movement, with the support to be displaced into its deposition position. The effect of this is that supports with any sheets thereon which stand in the way of a support being moved into its deposition position are automatically moved out of the way provided there is still room where the support requiring to be moved away can be moved away.